Packaging is the technology of enclosing or protecting items, remains, or products for transport, distribution, storage, sale, and/or use. Packaging material can come in a wide range of structures, sizes and material. One objective of most types of packaging is providing physical protection from hard contact, heat, cold, compression, and other mechanical or electrically shock. Another objective of many types of packaging is providing barrier protection from chemical exposure, oxygen, water vapor, dust, etc. A further objective of most types of packaging is to contain or agglomerate the contents being packaged. For example, small objects are typically grouped together in one package for reasons of efficiency. Additionally, some items such as liquids, powders, and granular materials need containment.
Plastic packaging is used to achieve many of these objectives. For example, plastic sheeting can be used to form plastic bags that can serve a wide range of purposes. However, the plastic bags that are formed from the plastic sheeting are generally created by a heat sealing process that seals the bag closed once the items to be packaged are placed in the bag. The heat seal method can be cumbersome and depending on the items being packaged, the heat used to seal the bags can disturb the contents therein. This is especially true for individual packages that are custom made to different sized items such that the packages are made around the item.
Adhesives can be used to adhere plastic sheets together, but the placement of the adhesive has to be very precise because generally such adhesives stick indiscriminately to most everything the adhesives contact. Thus, if the use of the adhesive is not precise, the adhesive may stick to the items placed in the bag.
Cohesives, which are often referred to in the industry as self-seal, cold seal, or cold seal adhesives, were thought to be a good alternative since, once they are cured on a substrate, they only stick together to form a seal when portions of the cohesive come in contact with each other. Cohesives, however, have been used on plastic sheeting to very limited success. In particular, the cohesive has to be aggressive enough to stick to one surface of a plastic sheet, but passive enough, once cured, to not stick to the opposing surface of the plastic sheet when bundled for transport, such as, for example, when rolled onto a roll. Since the surfaces of the plastic sheet are composed of the same material, finding the fight balance of tack for the cohesive is extremely hard to accomplish. If the cohesive is too aggressive, the cohesive will stick to both the surface to which it was applied and cured and to the opposing surface when the plastic sheeting is rolled onto a roll thereby causing blocking. If the cohesive is too passive, it will not stick to the surface to which it was applied and cured rendering the plastic sheet useless for its intended purpose. To combat this issue, one surface of the plastic sheet may be dyne treated, i.e., provided with a corona treatment, to create a difference in the surfaces such that a cohesive is more likely to securely attach to the treated surface than the untreated opposing surface of the plastic sheet. Even with the difference in the treated surface and the untreated opposing surface, the window within which the cohesive can properly operate is small.
Therefore, a need exists for packaging sheets and material that can be sealed without the need for exposure to heat and that still provides a seal that does not break easily and prevents the leakage of the contents being sealed within the packaging formed by the packaging sheets and material.